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The various dissociation thresholds of phenol···Ar3complexes for the consecutive loss of all three Ar ligands were measured in a molecular beam using resonant photoionization efficiency and mass analyzed threshold ionization spectroscopy via excitation of the first excited singlet state (S1). The adiabatic ionization energy is derived as 68077 ± 15 cm−1. The analysis of the dissociation thresholds demonstrate that all three Ar ligands in the neutral phenol···Ar3tetramer are attached to the aromatic ring via π-bonding, denoted phenol···Ar3(3π). The value of the dissociation threshold for the loss of one Ar ligand from phenol···Ar3(3π), ∼190 cm−1, is significantly lower than the binding energy measured for the π-bonded Ar ligand in the phenol···Ar(π) dimer, D0= 535 ± 3 cm−1. This difference is rationalized by an ionization-induced π → H isomerization process occurring prior to dissociation, that is, one Ar atom in phenol···Ar3(3π) moves to the OH binding site, leading to a structure with one H-bonded and 2 π-bonded ligands, denoted phenol···Ar3(H/2π). The dissociation thresholds for the loss of two and three Ar atoms are also reported as 860 and 1730 cm−1. From these values, the binding energy of the H-bound Ar atom can be estimated as 870 cm−1. [ABSTRACT FROM AUTHOR]